1. Field of the Invention
The present invention relates to a charge-pump circuit, and more particularly, to a charge-pump circuit having a convertible discharging path.
2. Description of the Prior Art
A charge-pump circuit is utilized for generating a required output voltage, and is one of the most important elements in a displaying apparatus. Please refer to FIG. 1. FIG. 1 is a diagram illustrating a conventional charge-pump circuit 100. The charge-pump circuit 100 includes a first input switch SW1, a second input switch SW2, a first output switch SW3, a second output switch SW4, a charging capacitor C1, and a pumping capacitor C2. A node N1 of the first input switch SW1 receives the input voltage Vi, and a node N2 of the second input switch SW2 is coupled to a first ground reference voltage Vg1. The charging capacitor C1 is coupled between nodes N3 and N4, and the pumping capacitor C2 is coupled between nodes N5 and N6, in which the node N5 is utilized for outputting the output voltage Vo and the node N6 is coupled to a second ground reference voltage Vg2. Furthermore, the first output switch SW3 is coupled between the nodes N3 and N5, and the second output switch SW4 is coupled between the nodes N4 and N6.
According to the conventional charge-pump circuit 100, when the first input switch SW1 and the second input switch SW2 are switched on, the electric charge corresponding to the voltage difference between the input voltage Vi and the first ground reference voltage Vg1 is charged to the charging capacitor C1. Meanwhile, the first output switch SW3 and the second output switch SW4 are switched off. Then, the first output switch SW3 and the second output switch SW4 are switched on to pump the electric charge to the pumping capacitor C2. By appropriately setting the second ground reference voltage Vg2, the output voltage Vo that is required in the displaying circuit can be generated.
In general, each charge-pump circuit is only able to generate a specific output voltage. When different output voltages are required in the displaying apparatus, a plurality of charge-pump circuits are needed. The charging capacitor C1 and the pumping capacitor C2 in the charge-pump circuit occupy a large area and significantly increase the cost of the charge-pump circuit. Therefore, lowering the occupied area and cost of each charge-pump circuit is an urgent problem in this field.